The manufacture of semiconductors involves subjecting a substrate, for example a silicon wafer, to a series of processes. Depending on the nature and purpose of the device, a large number of processes can be involved, including heat treating, deposition, etching, patterning, and other processes. Each of these processes can include a number of process steps. Twenty or thirty or more mask layers and a hundred or more process steps can be involved. Most of these steps are temperature sensitive, requiring precise temperature control and temperature uniformity across the surface of the wafer.
Temperature control in semiconductor wafer processing can be carried out by preprogramming process parameters, or by using closed or open loop temperature control systems. Typically, some form of temperature sensors are used to monitor process chamber temperature or substrate support temperature. Often an in-chamber temperature probe is used to sense the temperature of the gas in the chamber or that of a plasma when one is present. Alternatively, a pyrometer or other radiation type sensor or optical sensor is used to measure gas temperature or the temperature of the wafer being processed. Temperature sensors are often included in the substrate support or the substrate heating plate to monitor and control the support temperature or to approximate the temperature of a supported wafer. None of these methods is perfect in determining the actual temperature of a wafer during processing, and particularly in determining temperature variations or uniformity across the wafer surface during processing.
To predict wafer temperature during processing, often calibration wafers are used that are run through actual processes. These calibration wafers have probes which have been fixed to test wafers to monitor temperatures and temperature variations and profiles throughout the course of a process or series of process steps. For example, U.S. Pat. Nos. 6,889,568, 7,135,852 and 7,151,366 disclose the use of temperature sensors placed on or in a calibration or test wafer. With such systems, simulated temperature conditions can be monitored by the calibration or test wafer and temperature tables can be stored in memory and correlated with the process parameters that were used to generate them. As such, wafer temperature can be estimated indirectly, by measuring those other parameters and consulting the tables. For accuracy, these systems depend on the conditions of the actual process corresponding exactly to the conditions that existed when the test wafer was measured.
Lack of accuracy in the monitoring or control of the actual temperatures of wafers during processing, as well as the temperature uniformity across the wafers, can result in loss of quality in the wafers being processed and the semiconductor circuits and devices being manufactured.
Accordingly, there remains a need to more accurately determine and control the temperatures on the surfaces of semiconductor wafers during processing.
The embodiments, objectives and advantages of the invention will be more readily apparent from the following detailed description, in which: